The effect of ultrasound on the electrochemical loading of hydrogen in palladium
A. Wark · S. Crouch-Baker · M.C.H. McKubre · F.L. Tanzella
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In one page
Everything in this field runs on one number: how much hydrogen you can force into a palladium electrode. Michael McKubre’s SRI International group, with Alan Wark of Strathclyde, asked what ultrasound does to that number — a fair question, since sound is known to shake loose whatever is stuck to an electrode surface. They ran palladium wires in ordinary electrolysis cells suspended in a 20 kilohertz ultrasonic bath, and read the loading continuously off the wire’s own electrical resistance. The answer was blunt and useful: sound makes the loading go down. Applying ultrasound to a well-loaded electrode drives hydrogen back out, the cell voltage falls with it, and extended sonication settles every cell at about 0.75 to 0.8 hydrogen atoms per palladium atom no matter where it started. Switch the sound off and the wire reloads, but not all the way back. The team’s reading is that ultrasound strips away the trace surface species that make high loading possible in the first place.
Why it matters hereChapter 12 turns on loading — McKubre’s own work makes the highest loading a cathode ever reaches the single best predictor of whether it will make heat — so anything that sets the ceiling on loading sets the entrance to the whole field. This paper shows the ceiling is not a bulk property of palladium but a property of a few adventitious species sitting on its surface, which is why the same recipe works in one laboratory and fails in the next, and where an experimenter should look to gain control.
What it claims
01The primary consequence of applying ultrasound to a well-loaded, cathodically polarized palladium electrode is a decrease in loading, with a closely parallel decrease in the measured cell voltage. The effect was found in both acidic and basic electrolytes — 1 molar sulphuric acid and 1 molar lithium hydroxide — at current densities of 52 and 104 milliamps per square centimetre.Section 3, Results, opening paragraph; Table 1, experiment chronology; Figures 2 to 4
Published and peer-reviewed02Two processes with widely different time constants are at work. First a relatively rapid drop, of order one hour, in both loading and cell voltage, in which the voltage change is more or less constant at 30 to 50 millivolts and independent of current density. Then an extended period in which loading falls slowly, with a parallel voltage fall, reaching a new steady state after a variable time of several tens of hours.Section 3, Results, second paragraph
Published and peer-reviewed03Extended sonication drives every cell to the same place. Although the total loading decrease during a given period of sonication is not strictly reproducible, the final loading on extended sonication is typically in the range 0.75 to 0.8 hydrogen atoms per palladium atom, regardless of the initial loading. Loading itself was read continuously from the cathode’s four-point electrical resistance against a calibrated resistance-versus-loading curve, the standard in situ method in this work.Section 3, Results, third paragraph; Section 1, Introduction, Figure 1
Published and peer-reviewed04The effect is not heating. A platinum cathode run under the same conditions serves as the thermometer: platinum’s known temperature coefficient of resistance turns its resistance change into a temperature change, giving about 5 degrees Celsius of warming under sonication, a figure independently confirmed by thermocouples placed in the electrolyte. The authors state that in this well temperature-controlled system the observed effects are too large to be entirely due to that small temperature rise. A virgin palladium sample sonicated with no electrochemical current showed no resistance change beyond the small thermal one.Section 3, Results, experiment IV and Figure 5, and closing paragraph; Section 4, Discussion, first paragraph
Published and peer-reviewed05The damage is not fully undone. On removal of the irradiation reloading occurs, typically completing within less than ten hours, but not to the original extent — to reload an electrode more completely a brief period of anodic current, in the absence of irradiation, is usually necessary. The authors read this as evidence that what ultrasound removes is not adsorbed hydrogen itself but something else that does not re-form on its own.Section 3, Results, first and third paragraphs; Section 4, Discussion, fourth paragraph
Published and peer-reviewed06The interpretation names the real control variable. Loading at a fixed current is set by the chemical potential of hydrogen adsorbed on the surface — for reference, going from 0.7 to 1.0 hydrogen per palladium adds roughly 300 millivolts to the cathode overvoltage at room temperature. Reaching loadings above about 0.8 by aqueous electrochemistry requires more than a clean, catalytically active surface: it requires inhibitors, so-called surface poisons, that impede the recombination of adsorbed hydrogen atoms. No such agent was added deliberately here, and the authors assign the loading loss to ultrasound stripping those adventitious species away — which, they note, is also consistent with the irreproducibility such experiments are known for.Section 4, Discussion, second through fifth paragraphs
Published and peer-reviewed
The way in
https://doi.org/10.1016/s0022-0728(96)04767-5Journal of Electroanalytical Chemistry 418 (1996) 199 to 204, a short communication received 8 January 1996 and revised 8 April 1996. The record is closed access under the Elsevier text-and-data-mining user licence, so none of the paper is reproduced on this page. The full six-page text was read for this sheet on 2026-09-08 from the LENR-CANR library copy at lenr-canr.org/acrobat/WarkAWtheeffecto.pdf, and every locator below cites that text by the paper’s own numbered sections, figures and table. A. Wark wrote from the Department of Pure and Applied Chemistry, University of Strathclyde, Glasgow, as an SRI visiting scientist; S. Crouch-Baker, M. C. H. McKubre and F. L. Tanzella from the Energy Research Center, SRI International, Menlo Park, California. The work was funded by NEDO and the Institute of Applied Energy, Japan.
How to cite it
A. Wark, S. Crouch-Baker, M.C.H. McKubre, F.L. Tanzella (1996) The effect of ultrasound on the electrochemical loading of hydrogen in palladium. doi:10.1016/s0022-0728(96)04767-5
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